This grant focuses on the investigation of the fragile X mental retardation protein (FMRP) interactions with G quartet forming RNA target(s). Fragile X syndrome is the most common form of inherited mental retardation, affecting ~ 1 in 4000 males and ~ 1 in 8000 females. The syndrome is caused by the loss of a normal cellular protein (FMRP), which is thought to act as a translational repressor of specific messenger RNA (mRNA). Although the in vivo RNA targets of the protein remain elusive, it has been reported that FMRP binds with high affinity to RNA sequences rich in guanine content, which fold into G quartet structures. Given the importance of the FMRP RNA binding activity for its function, one of the specific aims of this grant is to investigate the molecular basis of RNA recognition by FMRP. Is the G-quartet containing RNA recognized via a sequence specific, via a structure specific mechanism, or both? Is FMRP stabilizing or destabilizing these structures? FMRP binds the G quartet forming RNA using its arginine-glycine rich domain (RGG box), a domain found in many other RNA binding proteins. Another aim of the proposal is to determine the level of specificity with which the G quartet structures are recognized by this domain, by analyzing the interactions of 2 different RGG boxes derived from other RNA binding proteins with these RNA sequences. The third aim of the proposal is to determine if protein arginine methylation, a common posttranslational modification involving the methylation of arginine residues within the RGG box, plays a role in modulating the FMRP-RNA interactions. Answers to such questions will contribute to our ability to identify the in vivo targets of FMRP, in an effort to understand the link between the absence of the protein and the phenotype of the fragile X syndrome. To accomplish these goals, molecular biology and biochemistry methods will be used to produce the RNA and protein and biophysical techniques such as NMR spectroscopy, fluorescence spectroscopy, UV-Vis spectroscopy will be employed to study these biomolecules and their interactions.